Experimental study of flame propagation in propane-air mixture near rich flammability limits in microgravity

The experiments were carried out in a cylindrical closed vessel of 8.5-L capacity, made of transparent organic glass. Propane air mixture was used; pressure history was measured. A high-speed video camera recorded the history of flame propagation. During the experiments the vessel was located inside the cage of a drop-tower assembly. The microgravity experiments started with ignition of the flammable mixture at the bottom or central part of the vessel. The video camera registered changes in flame development while pressure records indicated corresponding changes in heat release rate. The microgravity experiments were compared with similar experiments conducted under normal gravity conditions. Behavior of flame propagation was investigated in detail for mixture concentrations between 6.4% and 9.5% C3H8. It was found that the flammability limit under microgravity conditions was close to the limit for upward-propagating flame at 19 (9-0% C3H8 versus 9.5% C3H8 at 1 g). However, the behavior of flame propagation and pressure history was completely different: Under microgravity the flame was not visible but combustion was indicated by pressure rise.